Several different polymerization processes are commercially employed for the preparation of ethylene polymers, including those known to persons skilled in the art as "high pressure", "gas phase", "solution" and "slurry".
This invention relates to a slurry polymerization process. In a conventional slurry polymerization process, a "supported" catalyst (i.e. a catalyst which is deposited on a support) is used to initiate ethylene polymerization in a hydrocarbon diluent. The hydrocarbon diluent does not completely dissolve the resulting polymer, thereby creating a slurry of dispersed polymer particles (hence the term "slurry" process). The so-called "Phillips" slurry process for ethylene polymerization is widely reported to use a catalyst consisting of a chromium complex deposited on a metal oxide (such as silica or alumina) and isobutane as the diluent.
A slurry polymerization process which uses a phosphinimine-cyclopentadienyl catalyst in a conventional form (i.e. in supported form) for the preparation of ethylene polymers is disclosed in a copending and commonly assigned patent application (Stephen et al).
We have now discovered that an unsupported phosphinimine-cyclopentadienyl type catalyst may be advantageously used in a slurry polymerization process, thereby eliminating the need to prepare the catalyst in supported form and allowing simple, inexpensive catalyst addition systems to be utilized.